KETTLE-HOLE DEVELOPMENT FOLLOWING THE 2010 GLACIAL OUTBURST FLOOD AT GIGJOKULL, EYJAFJALLAJOKULL, ICELAND: AN ESTIMATION OF ICE LOSS?

Glacial outburst floods (GLOFs) are a complex geologic event arising from rapid ice melting or ice-dam failure with pitted outwash plains as a key identifier of their activity. Gígjökull, a northern outlet glacier of Eyjafjallajökull, experienced a series of GLOFs following a subglacial volcanic eruption in Iceland in early 2010. Gígjökull’s forefield went from a ~15 gigaliter proglacial lake to a braided stream network, a series of topographic inversions, known as kettles, and a developing desert pavement. Using kettles as a gauge for brittle-ice loss, ~80% of exposed kettles (n=118) were studied along a 315m transect, atop elevated desert pavement, starting approximately 500m from the glacier. Acquired kettle data included diameter and depth measurements (and calculated right-circular conical volumes), kettle hole stratigraphy, and observations of shape and/or evidence of recent sediment movement (e.g., tensional cracks, vertical walls). The mean kettle diameter was 2.9m (σ=1.7); mean depth was 0.9m (σ=0.4); mean calculated volume was 4.0m³ (σ=9.7). A positive linear trend between increasing kettle depth and increasing kettle diameter was found (r²= 0.7588). Despite localized clusters of 10-20 kettles showing a positive relationship between calculated volume and proximity to the glacier, no overall trend was found. Using available photogrammetric data since the GLOF (i.e., Google Earth, 2012 and 2013; TerraServer, 2016) combined with kettle data, three post-GLOF landscape-change maps were generated. Recorded kettle development, from 2012 to 2017, is diachronous with kettle count increasing with distance from the glacier. Assuming a 1:1 volume ratio of ice block to kettle depression, the minimum total of buried ice is ~500m³; a negligible value confirmed by video footage of the GLOF. Because the GLOF at Gígjökull was volcanically induced, glacial ice was likely melted away rather than broken and buried. The use of pitted outwash plains as a key characteristic of GLOFs, therefore, is probably better suited to moraine- or ice-dam failures, which likely generate more ice blocks for kettle development.